Differing from thin-film-transistor liquid-crystal display (TFT-LCD) devices which rely on backlight systems for light emission, organic light-emitting display devices emit light by themselves and hence provide higher visibility and brightness and can be made thinner. At present, organic light-emitting display devices are praised as the next generation display devices that will replace the TFT-LCD devices.
Reference is now made to FIG. 1 which shows a circuit diagram of a pixel in an organic light-emitting display device of the prior art. As shown in FIG. 1, each pixel in the organic light-emitting display device includes a pixel circuit 10 and an organic light-emitting diode OLED. The pixel circuit 10 is connected to a data line Dm and a scan line Sn so as to control light emission of the organic light-emitting diode OLED. The pixel circuit 10 includes a switch thin-film transistor M1, a drive thin-film transistor M2 and a capacitor Cst. The switch thin-film transistor M1 has a gate connected to a scan line Sn and a source connected to a data line Dm. The drive thin-film transistor M2 has a gate connected to a drain of the switch thin-film transistor M1, a source connected to a first power source ELVDD via a first power wiring (not shown) and a drain connected to an anode of the organic light-emitting diode OLED. A cathode of the organic light-emitting diode OLED is connected to a second power source ELVSS via a second power wiring (not shown). The organic light-emitting diode OLED emits light under the effect of a current provided by the pixel circuit 10. The capacitor Cst is connected between the gate and source of the drive thin-film transistor M2 in order to maintain a digital signal at the gate of the switch thin-film transistor M1 and a threshold voltage of the drive thin-film transistor M2 over a predetermined period of time.
However, during the manufacturing process of the thin-film transistors, variations may occur in their threshold voltages. Such variations in threshold voltages of the thin-film transistor that act as driving elements may lead to the organic light-emitting diode OLED emitting light with different brightness levels in response to the digital signal which is, however, indicative of the same brightness level. This may lead to brightness non-uniformity and hence reduced display quality.
Further, the power wiring connecting the first power source ELVDD and the pixel circuits 10 have certain impedances which lead to voltage drops when currents flow in them and hence uneven positive power source voltages supplied to the pixel circuits 10, thus further reduce brightness uniformity. Another factor that may deteriorate the problem of non-uniform brightness is light-emission efficiency degradation of the organic light-emitting diodes OLED due to their aging over time.